1. Field of the Invention
The present invention relates to a liquid electrophotographic printer, and more particularly, to a cleaning apparatus for removing various contaminants containing untransferred toner remaining on a photoreceptor belt and/or a transfer roller after printing, using a cleaning member having a solvent, and a liquid electrophotographic printer having the cleaning apparatus.
Here, printers generally refer to all kinds of image printing apparatuses for printing an image using an electrophotographic process, for example, copiers, facsimile apparatuses or the like, as well as general laser printers.
2. Description of the Related Art
In general, a liquid electrophotographic printer forms an electrostatic latent image on a photosensitive medium such as a photoreceptor belt by scanning a laser beam onto the photoreceptor belt, develops the electrostatic latent image formed on the photoreceptor belt using a developer liquid, which is a mixture of solid toner of a predetermined color and liquid carrier serving as a solvent, and transfers the developed image to a printing sheet, thereby printing a desired image.
The liquid electrophotographic printer typically have two parts; an engine which consists of essential parts for performing a printing process, and a controller for interpreting data transmitted from a data outputting device such as a computer, constructing to-be-printed image data by individual bits of a one-page size to then be stored in a video RAM, communicating with the engine so as to perform printing and then transmitting the data stored in the video RAM to the engine in the form of serial data.
An exemplary liquid electrophotographic printer having the aforementioned configuration is schematically shown in FIG. 1, which will now be described briefly.
As illustrated, the liquid electrophotographic printer includes a photoreceptor belt 10 wound around and supported by rollers 1, 2 and 3 which are installed within a printer body and traveling along a predetermined track.
In the neighborhood of the photoreceptor belt 10 are installed an erasure unit 20 for erasing the surface potential formed on the photoreceptor belt 10, a charging unit 30 for charging the photoreceptor belt 10 from which the surface potential has been erased, to a predetermined potential, an exposure unit 40 for forming an electrostatic latent image by scanning a laser beam converted according to electric data of a portion to be printed, onto the photoreceptor belt 10, a development unit 50 for supplying a developer liquid, which is a mixture of solid toner and liquid carrier, to the photoreceptor belt 10 to thus adhere the toner to a portion of the surface of the photoreceptor belt 10 where the electrostatic latent image is formed, thereby forming a visible image, a drying unit 60 for absorbing only the carrier contained in the developer liquid other than the toner adhered to the photoreceptor belt 10, drying and removing the same, a transfer/fixation unit 70 for transferring the toner formed on the photoreceptor belt 10 as an image, to a printing sheet 80.
Inside the photoreceptor belt 10 are installed a plurality of backup rollers 4, 5, 6 and 7 in close contact with the photoreceptor belt 10 to then be passively driven.
Also, the exposure unit 40 includes four laser scanning units (LSUs) 41, 42, 43 and 44 corresponding to various colors, for example, yellow (Y), magenta (M), cyan (C) and black (K), respectively.
The development unit 50 includes four development rollers 51, 52, 53 and 54 rotating selectively in close contact with the photoreceptor belt 10, and squeegee rollers 51', 52', 53' and 54' installed next to the development rollers 51, 52, 53 and 54, respectively.
The drying unit 60 includes a dry roller 62 rotatably installed in a bracket (not shown) provided inside a manifold 61, and a pair of heating rollers 63 and 63' selectively in close contact with the dry roller 62.
The transfer/fixation unit 70 includes a transfer roller 71 selectively brought into close contact with the photoreceptor belt 10, and a fixation roller 72 selectively brought into close contact with the transfer roller 71. The printing sheet is fed between the transfer roller 71 and the fixation roller 72. At this stage, the image transferred to the transfer roller 71 is conveyed to the printing sheet 80. The fixation roller 72 fuses the toner image to then be adhered to the printing sheet 80 by applying heat and pressure to the toner image conveyed to the printing sheet.
Although not shown, the liquid electrophotographic printer further includes a developer liquid supplying device for continuously supplying a developer liquid having a predetermined concentration to the development unit 50, a sheet feeding unit for supplying printing sheets and a sheet ejection unit.
The printing process of the aforementioned liquid electrophotographic printer is performed as follows.
If a printing instruction is input from a data outputting device such as a computer, the erasure unit 20 first operates to electrically clear the residual charges remaining on the photoreceptor belt 10. Then, the charging unit 30 applies a high voltage to the photoreceptor belt 10 to charge the surface thereof to a predetermined potential (generally 500 to 700 V).
Next, the exposure unit 40 scans a laser beam converted according to the electric data of a portion to be printed on the photoreceptor belt 10 charged to the predetermined potential, thereby forming an electrostatic latent image on the photoreceptor belt 10 due to a difference in the surface potential.
After exposure, the development unit 50 performs development, in which the electrostatic latent image formed on the photoreceptor belt 10 is converted into a visible image using toner particles. The development unit 50 adheres the toner contained in an externally supplied developer liquid to the portion of the photoreceptor belt 10 where the electrostatic latent image is formed, thereby forming the visible image on the photoreceptor belt 10. Here, the liquid carrier contained in the developer liquid is squeezed simultaneously with development to then be primarily separated for removal.
The surplus carrier which is not removed by the development unit 50 is absorbed by the dry roller 62 while the photoreceptor belt 10 passes through the drying unit 60, and then evaporated by a pair of heating rollers 63 and 63' for removal, so that the toner image formed on the photoreceptor belt 10 becomes a suitable image to be transferred.
The toner image developed on the photoreceptor belt 10 through the above-described process is transferred to the transfer roller 71 via the transfer/fixation unit 70. The image transferred to the transfer roller 71 is conveyed to the printing sheet 80 fed between the transfer roller 71 and the fixation roller 72, and are completely fused to then be fixed to the printing sheet 80 when heat and pressure are applied by the fixation roller 72.
During the above-described process, transferring an image, for example, from the photoreceptor 10 to the transfer roller 71 or from the transfer roller 71 to the printing sheet 80, is performed due to a difference in the surface energy, that is, a difference in the adhesion, between each of the photoreceptor belt 10, the transfer roller 71 and the printing sheet 80. In other words, since the adhesion of the photoreceptor belt 10 is set to be relatively higher than that of the transfer roller 71, and the adhesion of the printing sheet 80 is set to be higher than that of the transfer roller 71, the toner image of the photoreceptor belt 10 is transferred to the transfer roller 71 and is finally transferred to the printing sheet 80.
Here, it is desirable that the image of the photoreceptor belt 10 is completely transferred to the transfer roller 71 and that the image of the transfer roller 71 is completely transferred to the printing sheet 80. However, in an actual printing process, the adhesion between the photoreceptor belt 10 and the transfer roller 71 and the adhesion between the transfer roller 71 and the printing sheet 80 are not maintained at appropriate levels. Thus, some of the image of the photoreceptor belt 10 may remain on the photoreceptor belt 10, without being completely transferred to the transfer roller 71. Also, some of the image of the transfer roller 71 may remain on the transfer roller 71, without being completely transferred to the printing sheet 80.
As described above, in the case where untransferred toner remains on the photoreceptor belt 10, the toner may overlap with an image to be printed next, resulting in deterioration of picture quality. Also, if the untransferred toner is hardened on the photoreceptor belt, the portion of the photoreceptor belt bearing hardened toner cannot be used, which unavoidably causes deterioration of picture quality. Also, the toner remaining on the photoreceptor belt is used in development of a subsequent image to thus contaminate ink and also causes contamination to the dry roller. Thus, the untransferred toner remaining on the photoreceptor belt must be removed.
The aforementioned problems may also be encountered in the case where untransferred toner remains on the transfer roller 71. Moreover, since the contamination of the transfer roller 71 may adversely affect picture quality, the contamination of the transfer roller 71 must be eliminated.
To this end, in the conventional printer, as shown in FIG. 1, there is provided a cleaning apparatus for removing ink sludge sticking to or remaining on the transfer roller 71, by installing a separate cleaning roller 90 in the neighborhood of the transfer roller 71 to be selectively brought into close contact with the transfer roller 71. This cleaning apparatus can also be used for cleaning the photoreceptor belt 10 in the following manner.
That is to say, after printing, the fixation roller 72 is separated from the transfer roller 71 and then the untransferred toner remaining on the photoreceptor belt 10 is made to be transferred to the transfer roller 71 while operating the cleaning roller 90 in close contact with the transfer roller 71. Then, the transfer roller 71 is cleaned using the cleaning roller 90, thereby removing the contaminants, that is, untransferred toner, of the photoreceptor belt 10.
However, the aforementioned cleaning apparatus of a general liquid electrophotographic printer, which is configured such that untransferred toner remaining on a photoreceptor belt is first transferred to a transfer roller and the contaminants transferred to the transfer roller are then removed, has a problem in that there is a limit in removing the contamination of the photoreceptor belt, that is, the toner which is not transferred from the photoreceptor belt to the transfer roller during a cleaning process, cannot be removed.
Also, since the conventional cleaning apparatus is a dry type in which the surface of a transfer roller is wiped out by simply bringing a cleaning roller into close contact with the transfer roller, the contaminants containing untransferred toner remaining on a photoreceptor belt are not completely removed. Also, the adhesion of the transfer roller may be weakened so that the untransferred toner on the photoreceptor belt cannot be transferred to the transfer roller, thereby obstructing effective removal of contaminants of the photoreceptor belt.
Further, since the conventional cleaning apparatus is configured to remove contaminants of a photoreceptor belt by being driven in a separate cleaning mode after printing, a separate cleaning time is required. Thus, the overall time required for printing increases. Also, since the contamination of the photoreceptor belt cannot be removed during a continuous printing process, the deterioration of picture quality, which is due to contamination of the photoreceptor belt, cannot be avoided.